To analyze the behavior of a signal over a period of time, a block of time-related measurements is taken. A display of amplitude measurements versus time will produce a waveform of the signal's behavior.
Continuous time interval measurements on a signal provide a way to analyze characteristics of the signal in the modulation domain, i.e., the behavior of the frequency or phase of the signal versus time. This is different than classic ways of measuring and displaying data about signals. An oscilloscope shows amplitude versus time: the time domain. A spectrum analyzer shows amplitude versus frequency: the frequency domain.
Continuous time interval measurements make it simpler to study dynamic frequency behavior of a signal: frequency drift over time of an oscillator, the frequency hopping performance of an agile transmitter, chirp linearity and phase switching in radar systems.
An example of an instrument that generates this type of time stamp and continuous time interval data is described in "Frequency and Time Interval Analyzer Measurement Hardware", Paul S. Stephenson, Hewlett-Packard Journal, Vol. 40, No. 1, February 1989.
Instead of a traditional frequency counter's numeric display, the modulation domain analyzer uses a graphic display of frequency versus time to efficiently communicate the far greater information bandwidth to the operator. The change is analogous to the change from a voltmeter to an oscilloscope for voltage versus time measurements.
The measurement setup requirements for making and displaying a measurement in the modulation domain are potentially more confusing and intimidating for the operator, and therefore a method for automatically scaling the instrument parameters and the display for a particular input signal is desirable to make the instrument easier to use.
In measuring frequency modulated signals, there can be a tradeoff between using a measurement setup that gives the best resolution of the signal's frequency and a measurement setup that gives the best data of the dynamic behavior of the frequency. For a slowly modulated signal, measuring the frequency over a large number of cycles gives better resolution of the frequency. However, for a rapidly modulated signal, measuring over too many cycles can average out the modulation.